This invention relates to semiconductor processing equipment. More specifically it relates to carriers for semiconductor wafers.
As semiconductors have become larger in scale, that is, as the number of circuits per unit area has increased, particulates have become more of an issue. The size of particulates that can destroy a circuit has decreased and is approaching the molecular level. Particulate control is necessary during all phases of manufacturing, processing, transporting, and storage of semiconductor wafers. Particle generation during insertion and removal of wafers into carriers and from movement of wafers in carriers during transport needs is to be minimized or avoided.
Build-up and discharge of static charges in the vicinity of semiconductor wafers can be catastrophic. Static dissipation capability is a highly desirable characteristic for wafer carriers. Static charges may be dissipated by a path to ground through the carrier. Any parts that are contacted by equipment or that may contact wafers or that may be touched by operating personnel would benefit by a path to ground. Such parts of carriers would include the wafer supports, robotic handles, and equipment interfaces.
Visibility of wafers within closed containers is highly desirable and may be required by end users. Transparent plastics suitable for such containers, such as polycarbonates, are desirable in that such plastic is low in cost but such plastics do not have adequate static dissipative characteristics nor desirable abrasion resistance.
Materials for wafer carriers also need to be rigid to prevent damage to wafers during transport and also need to be dimensionally stable through varying conditions.
Conventional ideal carrier materials with low particle generation characteristics, dimensional stability, and other desirable physical characteristics, such as polyetheretherketone (PEEK), are not transparent, are relatively expensive, and are difficult to mold into unitary large and complex shapes such as carriers and containers.
Generally containers and carriers for storing and transporting wafers have been designed to transport and hold wafers in vertical planes. Such carriers, for example the H-bar carriers well known in the art (see FIG. 18), are typically configured for also allowing a carrier position with the wafers in a horizontal position for processing and/or insertion and removal of the wafers. In the horizontal position the wafers are conventionally supported by ribs or wafer guides that form the wafer slots and extend along the length of the interior sides of the carrier. The carrier side is partially curved or angled to follow the wafer edge contour. Such carriers contact and support the wafers along two arcs on or adjacent to the wafer edge.
Additionally the shift of conventional carriers from the vertical transport position to the horizontal insertion-removal-process position can cause wafer rattle, wafer shifting, wafer instability, particle generation and wafer damage.
The industry is evolving into processing progressively larger wafers, i.e., 300 mm in diameter, and consequently larger carriers and containers for holding wafers are needed. Moreover the industry is moving toward horizontal wafer arrangements in carriers and containers. Increasing the size of the carriers has exacerbated shrinkage and warpage difficulties during molding. Increased dependence upon robotics, particularly in the removal and insertion of wafers into carriers and containers, has made tolerances all the more critical. What is needed is an optimally inexpensive, low particle generating, static dissipative carrier god in which the wafers are stable, and consistently and positively positioned and which minimizes the transfer of any particles on the carrier to the wafers.
A wafer container for transporting or holding wafers in a horizontal axially aligned arrangement has minimal four point regions of wafer support at the edge portion of the wafers. A preferred embodiment has a first container portion and a closeable door. The first container portion has a first molded portion of a static dissipative material having an upright door frame with integral planar top portion. An integral bottom base portion with an equipment interface also extends from the door frame. A second molded portion has a transparent shell which connects to the door frame, to the planar top portion, and to the bottom base portion. Separately molded wafer support columns connect to the top planar portion and to the bottom base portion and include vertically arranged shelves with upwardly facing projection providing minimal point or point region contact with the wafers. The shelves include wafer stops to interfere with forward or rearward movement of the wafers when supported by the projections and to prevent insertion beyond a seating position. A side handle engaging both the first molded portion and the second molded portion operates to secure the molded portions together. A robotic handle connects to the planar top portion. The robotic handle, the wafer shelves, the side handles, and the door frame have a conductive path to ground through the machine interface.
An additional embodiment is a conventional H-bar wafer carrier with protrusions added to the top side of the wafer guides such that when the H-bar carrier is positioned with the plane of the wafers in a horizontal arrangement the wafers have minimal contact with the carrier by the beads or protrusions on the wafer guides.
A feature and advantage of the invention is that wafer support is provided with minimal and secure wafer contact by the carrier.
A further advantage and feature of the composite container embodiment of the invention is that the composite design allows optimal use of materials, such as the more expensive abrasion resistant and static dissipative materials, for example PEEK, for the portions of the container that contact the wafers or equipment, and the use of less expensive clear plastic, such as polycarbonate, for the structural support of the container and the viewability of the wafers in the container. Thus, molding parameters and material selection may be chosen for each separately molded part to optimize performance and minimize cost.
A further advantage and feature of the composite container embodiment of the invention is that the composite construction minimizes the negative effects associated with molding large carriers such as warpage and shrinkage.
A further advantage and feature of the composite container embodiment of the invention is that all critical parts may be conductively connected to ground through the equipment interface portion of the carrier.
A further advantage and feature of the invention is that wafers are passively held in a specific seating position by the suitable shaped shelves.
A further advantage and feature of the invention is that the composite container may be assembled and finally secured together using the lugs, tongues, and tabs associated with the side handle.
A further feature and advantage of the invention is that the wafer contact with the protrusions or beads reduce accumulation of particulate matter on the wafers by minimizing the transferring of such particulate matter by minimizing the wafer contact with the carrier.
A further feature and advantage of the invention is that the protrusions or extensions on the top side of the wafer guides-may be formed in a variety of configurations.
A further feature and advantage of a preferred embodiment of the invention is that minimal point contact minimizes rocking of the individual wafers and provides for greater variations in molding while still maintaining consistent and positive wafer positioning. The critical dimension to be maintained is the top of the protrusions as compared to the entire length of the contact area on convention wafer guides.